Technical Abstract:
Transportation-induced stress can result in the recrudescence of Salmonella from infected swine tissues and increase fecal shedding, a serious contamination issue on the farm and at the slaughter plant. Recent research has focused on the release of the catecholamine norepinephrine (NE) as a host signal during stress and the growth stimulating properties exerted by NE on enteric pathogens such as Salmonella enterica serovar Typhimurium. Exposure of S. typhimurium to NE in vitro enhances the association between Salmonella and the swine gastric epithelium in vivo (Toscano et al., CRWAD 2004). Additionally, NE exposure increased the survival of S. typhimurium 190-fold in an ex vivo swine stomach contents assay. To determine the transcriptome during exposure to NE, microarray analysis was performed on S. typhimurium grown in nutritionally poor SAPI minimal salts medium containing 30% serum in the presence or absence of norepinephrine. In the presence of NE, 207 genes were up-regulated and 119 were down-regulated. The expression for selected genes was confirmed by real-time RT-PCR. Up-regulated transcripts include genes for amino acid biosynthesis, aerobic respiratory pathways, the TCA cycle, motility and chemotaxis. The most striking feature of the transcriptional profile is that at least 29 of the NE down-regulated genes are regulated by Fur (Ferric uptake regulator) and iron (including ent, fep, fes, fox and sit genes). Seven genes (fumAB, ftn, sodB and sdhABD) that are positively regulated by Fur and iron are induced in the presence of NE; these genes have been shown to be negatively regulated by the Fe**2+-Fur-repressed antisense RNA, ryhB. Although not represented on the microarray slide, we investigated the expression of ryhB using real-time RT-PCR. The ryhB antisense RNA is repressed 25.8 fold in the presence of NE. This analysis suggests that in the absence of NE, cells grow poorly due to inaccessibility of iron; however, in the presence of NE, iron is more readily available, facilitating cell growth and necessitating the synthesis of biosynthetic enzymes.